S5, league is only diverse now in role selection, viable champions are at an all time low
S5 was just before riot started nerfing for balance
so jungle was anything goes (pre-sated devourer TF being a viable pick in this era), top lane was tanks and bruisers with carrys still contesting before rework gangplank ruined everything, adc was the least diverse in terms of builds but that build was so good ANY ranged adc was viable, mid lane was mages and assassins, and support was mages and tanks
the only roles left out of s5 were heal/shieldsluts, ranged top laners, and utility junglers
now only bruisers, supports, and melee carrys (+ vlad, taliyah, and swain) are viable but you can play those in multiple roles which gives the impression of diversity but I personally wouldnt call vlad in top, mid, and adc "diverse"